I have never gottten it from the ghosts. Half my teams have gotten it from the chest in Bayjin, using this method ...1) approach Bayjin from the Mt Gigas side.
2) save game before you enter Bayjin for the first time.
3) Enter Bayjin, follow the ramp and kill the guy in the temple.
4) stand at the exit to the temple, aim at the 1st red dot to the right of the two green dots.
5) walk straight to the red dot
6) open the door and kill the guard
7) close the door
8) open the chest
9) If you get the sword, save game
10) if you don't get the sword but you get some good stuff (frontier phaser, light shield) save game USING A DIFFERENT NAME then reload from the savegame you made in step 2)
Repeat the process until you get the light sword or you get tired. Avoid battles, they slow you down. It can help to restart the game the next day. The random number generator doesn't reset completely when you reload.